The invention relates to a method and a device for camera-based monitoring of machines having mobile machine elements for collision prevention.
Modern industrial robots which move at considerable speeds may cause serious damage both to persons in the vicinity, the robots and to the work-pieces handled by them. This can lead to costly production stoppages. The safety of persons who interact with the automatically operating robots is has to be given the highest priority. In modern industrial robots or other machines with mobile machine elements, the movement of which represents a risk to persons and other objects, protective devices must therefore be used to prevent a collision taking place between the moving machine element and the object. To this end it is usually sufficient to bring the machine to rest before accidental contact takes place. The time from the shutdown command until it is at rest is referred to as the stopping time, and it determines the distance to be kept away from it.
Various sensors and evaluation methods to safeguard machine elements are known from the prior art. The simplest option consists in surrounding the machine with a fixed cage whose entrance (for example a door) is coupled to sensors so that the machine is stopped when the cage is entered. If there is a sufficient distance between the entrance and the moving machine, the latter will already be at rest before a person can come in contact with it.
Light barriers and light curtains which are arranged in the space around a moving machine and which transmit a shutdown signal to the machine when a light beam is interrupted, are widespread, but the design outlay is relatively high since the light emitters and sensors must be aligned accurately with one another.
German published patent application DE 103 58 770 A1 describes a safety system with which a machine and its vicinity can be monitored by a system comprising a plurality of cameras. The spatial position of object points in space can be determined by triangulation from synchronously recorded images. The machine is to be shut down if an amount of points lie in a previously defined volume. In contrast to the use of light barriers and arrays, virtually any volumes can be monitored in this way. Such volumes are static, however, and they can be activated or deactivated merely by program control.
In order for the distance between a person and a moving machine to be configured flexibly, German published patent application DE 102 26 140 A1 proposes to determine the present and prior articulation settings and articulation speeds for each individual robot articulation, and to derive a prediction from this relating to the configuration of a movement path of the robot during the stopping time. When deriving the movement path in the period of the stopping time, knowledge is also employed relating to the maximum speed and maximum negative acceleration of the moving machine components. In order to achieve real-time capability of the system despite the usually large number of parameters to be considered, it is proposed that the current stopping time and therefore the current stopping distance should be ascertained by means of a neural network. The distances between the mobile parts of the robot and persons/objects in its vicinity are recorded by means of sensors and are correlated with the ascertained stopping times or distances, so that a shutdown signal can be generated in the event of a collision risk.
Another safety system for an automatically operating machine is described by German published patent application DE 103 24 627 A1. Safety zones defined around the machine and monitored by sensors fitted on the machine are in this case adapted to the known instantaneous and future movement behavior. In the event that a person enters one of the safety zones, an estimate is made from the direction in which they are looking or from their movement behavior as to whether the entry into a safety zone is intentional or accidental. In the event of intentional entry, which is usually associated with planned intervention by the person with the working machine, the safety zones are modified.
In order to be able to estimate the correct stopping time or dimensioning of the safety zones at any time, in the methods known from the prior art it is necessary to employ data provided by the machine or its control program. This is possible only if the machine has a suitable data interface, via which all data required for dynamically safeguarding the machine are available. Often, however, such an interface is not available.